The same color illusion — also known as Adelson’s checker shadow illusion, checker shadow illusion and checker shadow — is an optical illusion published by Edward H. Adelson in 1995.[1] The squares A and B on the illusion are of the same color (or shade), although they seem to be different.

"When interpreted as a 3-dimensional scene, our visual system immediately estimates a lighting vector and uses this to judge the property of the material."[2]

Squares A and B have the same color.

The image below proves that the squares A and B have the same color.

A rectangle of the same color has been drawn connecting the two squares.

As a further example, the two "A"s are both the same color and do not change. The shadow is removed in two frames, and the colors of the chess board are reversed.